Grounding is an essential element of industrial electrical installations. Equipment is grounded not only to protect people that come into contact with the equipment but also to keep equipment from being harmed by fault currents, lightning strikes, the build-up of static electricity as well as electromagnetic interference and radio frequency interference. A grounding system can be as simple as ground wire tied to a single ground electrode driven into the ground or as complex as a ground grid network.
To determine that a good ground has been established and is maintained for an electrical installation, it is necessary to measure the impedance of the electrical system relative to earth ground. There are various methods to measure impedance including the traditional Fall of Potential method, which makes use of ground stakes, and the stakeless method, which makes use of a clamp on ground tester. Regardless of the method used, the measurement of a low ground impedance indicates a strongly grounded system. However, the value of the impedance that actually defines a low ground impedance has yet to be standardized. Various authorities have indicated that the system to ground impedance should be less than 5 Ohms while others have indicated that a system to ground impedance of less than 25 Ohms is acceptable.
Notably, the impedance to ground measurement methods noted above are performed with reference to an entire electrical system relative to ground. These methods do not provide the ability to test specific elements of the electrical system relative to earth ground, yet, such ability may be useful. For example, the ability to measure the ground impedance of a conduit system may be a desirable operational and safety precaution. Industrial electrical installations utilize conduit systems (e.g., various metal components including but not limited to metal conduits, fittings, housings, etc.) to protect underlying electrical wiring and electronics from exposure to detrimental environmental conditions. Because the conduit systems are made from metallic materials, their ability to conduct electricity themselves is of concern. Accordingly, care is taken to not only ground the circuits within the conduit system but to additionally ground the conduit systems themselves to help prevent the possibility of electrical shock and equipment malfunction.